Production of uniformly resin impregnated carbon fiber ribbon

ABSTRACT

An improved process is provided for the production of a continuous length of a carbon fiber ribbon which is impregnated with a tacky B-stage thermosetting resin. The fibrous ribbon undergoing treatment is resin impregnated with a neat liquid resin system of relatively high viscosity containing an A-stage thermosetting resin through the application of a force sufficient to bring the resin into intimate association with the individual fibers of the ribbon. The resin impregnated ribbon is next partially cured while continuously passing through a heating zone as described while interposed between a pair of flexible endless belts. The resulting ribbon is uniformly impregnated with a thermosetting resin of a tacky B-stage consistency and may be utilized in the formation of carbon fiber reinforced composite structures by filament winding or other suitable techniques.

United States Patent [191 Boss et al.

1451 Oct. 29, 1974 PRODUCTION OF UNIFORMLY RESIN IMPREGNATED CARBONFIBER RIBBON Monica, Calif.

[73] Assignee: Celanese Corporation, New York,

[22] Filed: Dec. 23, 1971 [21] Appl. No.: 211,339

[52] US. Cl 117/1l9.6, 117/65.2, 117/161 ZB, 117/228, 118/59, 118/70[51] Int. Cl B44d 1/48 [58] Field of Search 117/119.6, 161 ZB, 228,

117/65.2, DIG. 11; 118/59, 106; 34/116 [56] References Cited UNITEDSTATES PATENTS 1,905,959 4/1933 Cutler et al 118/106 2,419,922 4/1947Tippetts 117/7 2,528,168 10/1950 Paulsen 117/65.2 X 2,838,420 6/1958Valente 117/119.8 2,881,090 4/1959 Reidl et al. 117/161 ZB X 2,898,6648/1959 Salen 117/7 X 3,214,324 10/1965 Peerman.... 117/161 28 X3,271,350 9/1966 Vertnik 117/161 ZB X 3,382,086 5/1968 Singleton 117/7 X3,625,739 12/1971 Kaspar et al 117/65.2

3,677,804 7/1972 Kalnin et a1. 117/228 X 3,723,157 3/1973 Druin 117/161ZB FOREIGN PATENTS OR APPLICATIONS 710,750 6/1965 Canada 1l7/65.2525,037 5/1956 Canada 117/652 791,598 3/1958 Great Britain 1 17/228Primary Examiner-William D. Martin Assistant Examiner-Shrive P. Beck [57 ABSTRACT An improved process is provided for the production of acontinuous length of a carbon fiber ribbon which is impregnated with atacky B-stage thermosetting resin. The fibrous ribbon undergoingtreatment is resin impregnated with a neat liquid resin system ofrelatively high viscosity containing an A-stage thermosetting resinthrough the application of a force sufficient to bring the resin intointimate association with the individual fibers of the ribbon. The resinimpregnated ribbon is next partially cured while continuously passingthrough a heating zone as described while interposed between a pair offlexible endless belts. The resulting ribbon is uniformly impregnatedwith a thermosetting resin of a tacky B-stage consistency and may beutilized in the formation of carbon fiber reinforced compositestructures by filament winding or other suitable techniques.

19 Claims, 1 Drawing Figure PRODUCTION OF UNIFORMLY RESIN IMPREGNATEDCARBON FIBER RIBBON BACKGROUND OF THE INVENTION In the search for highperformance materials, considerable interest has been focused uponcarbon fibers. The terms carbon fibers or carbonaceous" fibers are usedherein in the generic sense and include graphite fibers which consistsubstantially of carbon and have a predominant X-ray diffraction patterncharacteristic of graphite. Amorphous carbon fibers, on the other hand,are defined as fibers in which the bulk of the fiber weight can beattributed to carbon and which exhibit a predominantly amorphous X-raydiffraction pattern. Graphite fibers generally have a higher Youngsmodulus than do amorphous carbon fibers and in addition are more highlyelectrically and thermally conductive.

As is known in the art, numerous precedures have been proposed in thepast for the conversion of various organic polymeric fibrous materialsto a carbonaceous form while retaining the original fibrousconfiguration essentially intact. Such procedures have in common thethermal treatment of the fibrous precursor in an appropriate atmosphereor atmospheres which is commonly conducted in a plurality of heatingzones, or alternatively in a single heating zone wherein the fibrousmaterial is subjected to progressively increasing temperatures. See, forinstance, U.S. Pat. No. 3,539,295 to Michael J. Ram for a representativeconversion process.

Industrial high performance materials of the future are projected tomake substantial utilization of fiber reinforced composites, andgraphitic carbon fibers theoretically have among the best properties ofany fiber for use as high strength reinforcement. Among these desirableproperties are corrosion and high temperature resistance, low density,high tensile strength, and high modulus.

Carbon fiber reinforced composites are commonly formed by coating orimpregnating carbon fibers with an uncured or partially cured liquidthermosetting resinous material which is ultimately to serve as thematrix or continuous phase in the composite article, converting theresinous material present on the carbon fibers to a tacky consistencythrough partial curing and/or evaporation of solvent, molding orotherwise shaping the same into the desired configuration, and fullycuring the same to form a rigid monolithic structure. Heretofore, athermosetting resinous material has commonly been applied to the carbonfibers from a solvent system which has necessitated volatilization ofthe solvent during the composite formation prior to complete curing.Additionally, techniques have been proposed wherein the thermosettingresin is applied from a liquid solventless system. Whenever filamentwinding is utilized to shape the composite article, the resinimpregnated carbon fibers bearing a partially cured resin must bynecessity be provided in an appreciable length. The efficient uniformresin impregnation, handling, and partial curing of continuous lengthsof carbon fibers particularly in ribbon form has been an elusive goalwhen employing prior art technology. Arch ovens have been employedwherein the resin impregnated ribbon is passed through a highlyelongated heating zone while supported upon one surface and the solventevaporated. The exposed surface accordingly tends to cure at a differentrate than the surface in contact with the support. If the resinimpregnated ribbon is unsupported over an appreciable span, ropingand/or splitting of the 5 same commonly occurs. A non-uniformly resinimpregnated or nonuniformly partially cured carbon fiber ribbon isincapable of yielding a carbon fiber reinforced composite structureconsistently exhibiting the required tensile properties for many end useapplications.

It is an object of the invention to provide an improved process for theproduction of a carbon fiber ribbon which is uniformly impregnated witha thermosetting resin which has a tacky B-stage consistency and issuitable for use in the formation of carbon fiber reinforced compositestructures.

It is an object of the invention to provide an im proved process forproduction of a continuous length of a thermosetting resin impregnatedcarbon fiber ribbon wherein the necessity to volatilize a solvent fromthe resin system in contact with the ribbon is eliminated.

It is an object of the invention to provide an improved process for theproduction of a continuous 5 length of a thermosetting resin impregnatedcarbon fiber ribbon wherein the partial curing of the resin is uniformlyaccomplished on a continuous basis within a limited area whilepreserving intimate association between resin and the carbon fiberribbon.

It is another object of the invention to provide an improved process forthe production of a carbon fiber ribbon which is uniformly impregnatedwith a thermosetting resin having a tacky B-stage consistency whereinthe single filament tensile properties initially exhibited by the carbonfiber ribbon are substantially unimpaired.

These and other objects, as well as the scope, nature, and utilizationof the invention will be apparent from the following description andappended claims.

SUMMARY OF THE INVENTION It has been found that an improved process forthe production of a uniformly resin impregnated ribbon of a carbonaceousfibrous material which is suitable for use in the manufacture of carbonfiber reinforced composite structures comprises:

a. continuously conveying to an impregnation zone a carbonaceous fibrousribbon containing at least about 90 percent carbon by weight,

b. forcing a liquid solventless system having a viscosity of about 500to 10,000 cps, comprising an A- stage thermosetting resin into intimateassociation with the carbonaceous fibrous ribbon while present in theimpregnation zone,

c. interposing the ribbon while in intimate association with thesolventless system between the outer surfaces of a pair of flexibleendless belts having a width greater than that of the ribbon,

d. continuously passing the ribbon in the direction of its length whileinterposed between the flexible endless belts through a substantiallyenclosed heating zone provided with a heated gaseous atmosphere whilesubstantially suspended therein wherein the belts and the ribbon arelooped in a single wrap about each of a multiplicity of rotatingparallel rollers wherein the inner surfaces of the belts are inalternating contact with the rollers as the belts and the ribbonprogress through the heating zone with the ribbon being out of contactwith the rollers and wherein the thermosetting resin in intimateassociation with the ribbon is converted to a B-stage consistency,

e. continuously withdrawing the ribbon from the heating zone whileinterposed between the outer surfaces of the pair of flexible endlessbelts and while the therrnosetting resin in intimate association withthe ribbon remains in a B-stage consistency, and

f. separating the resulting resin impregnated carbonaceous fibrousribbon from the flexible endless belts.

BRIEF DESCRIPTION OF DRAWING The drawing is a schematic presentation ofa representative apparatus arrangement capable of carrying out theprocess of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS The carbonaceous fibrous ribbonwhich serves as the starting material in the present process contains atleast about 90 percent carbon by weight. The carbon fibers of the ribbonmay exhibit either an amorphous carbon or a predominantly graphiticcarbon X-ray diffraction pattern. In a preferred embodiment of theprocess the carbon fibers contain at least about 95 percent carbon byweight and exhibit a predominantly graphitic X-ray diffraction pattern.

The width of the carbonaceous fibrous ribbon may conveniently vary fromabout 0.5 to 12 inches, or more.

The carbonaceous fibrous ribbon may comprise a single flat tow ofcontinuous carbon filaments or a plurality of substantially parallelmultifilament fiber bundles which are substantially coextensive with thelength of the ribbon.

In the latter embodiment the carbonaceous fiber bundles of the ribbonmay be provided in a variety of physical configurations. For instance,the bundles of the ribbon may assume the configuration of continuouslengths of multifilament yarns, tows, strands, cables, or similarfibrous assemblages. The multifilament bundles are preferably lengths ofa continuous multifilament yarn. The fiber bundles within the ribbonoptionally may be provided with a twist which tends to improve theirhandling characteristics. For instance, a twist of about 0.1 to 5 tpi,and preferably about 0.3 to l tpi, may be imparted to each fiber bundle.Also, a false twist may be used instead of or in addition to a realtwist. Alternatively, the fiber bundles may possess substantially notwist.

Multifilament fiber bundles may be provided within the ribbon in asubstantially parallel manner in the sub stantial absence of bundlecrossovers to produce a flat ribbon. The number of parallelmultifilament bundles present within the carbonaceous ribbon may bevaried widely, e.g., from 6 to 1,000, or more. In a preferred embodimentof the process a ribbon precursor is selected having a weft pickinterlaced with substantially parallel fiber bundles in accordance withthe teachings of commonly assigned U.S. Ser. No. 1 12,189, filed Feb. 3,1971 of K. S. Burns, G. R. Ferment, and R. C. Waugh which is hereinincorporated by reference. It is not essential, however, that theparallel fiber bundles or the filaments of a flat tow be bound by anyform of weft interlacement when constructing carbon fiber tapes forresin impregnation in accordance with the present invention.

The carbonaceous ribbon which serves as the starting material in thepresent process may be produced in accordance with a variety oftechniques as will be apparent to those skilled in the art. Forinstance, organic polymeric fibrous materials which are capable ofundergoing thermal stabilization may be initially stabilized bytreatment in an appropriate atmosphere at a moderate temperature (e.g.,200 to 400 C. and subsequently heated in an inert atmosphere at a morehighly elevated temperature, e.g., 900 to 1.000 C., or more, until acarbonaceous fibrous material is formed. If the thermally stabilizedmaterial is heated to a maximum temperature of 2,000 to 3,100 C.(preferably 2,400 to 3,100 C.) in an inert atmosphere, substantialamounts of graphitic carbon are commonly detected in the resultingcarbon fiber, otherwise the carbon fiber will commonly exhibit asubstantially amorphous x-ray diffraction pattern.

The exact temperature and atmosphere utilized during the initialstabilization of an organic polymeric fibrous material commonly varywith the composition of the precursor as will be apparent to thoseskilled in the art. During the carbonization reaction elements presentin the fibrous material other than carbon (e.g., oxygen and hydrogen)are substantially expelled. Suitable organic polymeric fibrous materialsfrom which the carbonaceous ribbon may be derived include an'acrylicpolymer, a cellulosic polymer, a polyamide, a polybenzimidazole,polyvinyl alchol, etc. Acrylic polymeric materials are particularlysuited for use as precursors in the formation of the carbonaceousribbon. Illustrative examples of suitable cellulosic materials includethe natural and regenerated forms of cellulose, e.g., rayon.Illustrative examples of suitable polyamide materials include thearomatic polyamides, such as nylon 6T, which is formed by thecondensation of hexamethylenediamine and terephthalic acid. Anillustrative example of a suitable polybenzimidazole ispoly-2,2-mphenylene-5,5' bibenzimidazole. Preferred carbonization andgraphitization techniques for use in forming the carbonaceous ribbon aredescribed in commonly assigned U.S. Ser. Nos. 777,275, filed Nov. 20,1968 of Charles M. Clarke (now abandoned); 17,780, filed Mar. 9, 1970 ofCharles M. Clarke, Michael J. Ram, and John P. Riggs (now U.S. Pat. No.3,677,705); and 17,832, filed Mar. 9, 1970 of Charles M. Clarke, Michael.1. Ram, and Arnold J. Rosenthal. Each of these disclosures is hereinincorporated by reference.

The carbonaceous ribbon optionally may be surface treated in order toimprove its ability to bond to a thermosetting resinous material.Conventional surface modification techniques may be selected. Preferredsurface modification treatments are disclosed in commonly assigned U.S.Ser. Nos. 65,454 and 65,456, (now U.S. Pat. No. 3,723,150) filed Aug.20, 1970 of M. L. Druin, G. R. Ferment. and N.V.P. Rao.

In the process of the present invention the carbonaceous ribbon iscontinuously conveyed to the impregnation zone while in a flatconfiguration. The ribbon may be conveyed in accordance withconventional fiber advancing techniques, and is preferably under auniform tension across its width when it arrives at the impregnationzone.

While present in the impregnation zone, a liquid solventless system of arelatively high viscosity comprising an A-stage thermosetting resin isforced into intimate association with the individual fibers of theribbon. The solventless system exhibits a viscosity of about 500 to10,000 cps. and preferably a viscosity of about 1,000 to 3,000 cps,during impregnation. It has been found that such resin systems ofrelatively high viscosity are capable of producing a more uniformlyresin impregnated ribbon.

The solventless system comprising an A-stage thermosetting resin is aflowable liquid and is substantially uncured during the impregnationstep. Such a material when exposed to heat hardens or sets to a rigidsolid consistency designated as a C-stage thermoset resin, and may notsubsequently be rendered plastic or flowable upon the reapplication ofheat. The curing or hardening of the thermosetting resin is broughtabout by heat-promoted chemical changes which result in the formation ofa compact, often crossl inked systen i lt is for use in the process ofthe invention. The epoxy resins utilized in the present invention aremost commonly prepared by the condensation of bisphenol A (4.4isoproplidene diphenol) and epichlorohydrin. Also, other polyols, suchas aliphatic glycols and novolac resins may be reacted withepichlorohydrin for the production of epoxy resins suitable for use inthe present proaccordingly essential that thermosetting resins be moldedto the desired configuration prior to the point in time when the curingreaction has progressed to the C-stage. A B-stage thermosetting resin isdefined as a partially cured thermosetting resin which has neither theconsistency of a flowable liquid, nor the consistency of a rigid solid.A B-stage thermosetting resin is accordingly soft and tacky in itsconsistency and may be readily molded. Upon the passage of time even atroom temperature, a B-stage thermosetting resin will assume a C-stageconsistency.

The solventless system applied in the impregnation zone may comprise theA-stage thermosetting resin, one or more curing agents for thethermosetting resin, one or more accelerators and one or more solidparticulate inert fillers. Conventional solvents such as acetone whichmay dissolve the A-stage thermosetting resin are to be avoided, sinceupon evaporation such solvents tend to produce strength-reducing voids,and also lengthen the period of time required for the A- stagethermosetting resin to assume a B-stage consistency within the heatingzone (described in detail hereafter). If desired, various modifiers ordiluents of the reactive type may be present within the solventlesssystem since such components form a permanent portion of the hardenedthermoset resin, and it is not essential to evaporate the same duringthe curing reaction.

The resin employed in the solventless system may generally be selectedfrom those thermosetting resins utilized in the production of fiberreinforced composites by prior art techniques. It is, of course,necessary that a substantially uncured thermosetting resin be selectedwhich inherently possesses the required viscosity at the impregnationtemperature or which may be modified to possess the required viscosityat the impregnation temperature by the addition of a reactive modifieror diluent. Illustrative examples of suitable thermosetting resins foruse in the present process include epoxy resins, phenolic resins,polyester resins, polyimides, etc.

An epoxy resin is the preferred thermosettingresin where n variesbetween zero and a small number less than about 10. When n is zero, theresin is a very fluid light-colored material which is substantially thediglycidyl ether of bisphenol A. As the molecular weight increases, sogenerally does the viscosity of the resins. Accordingly, theparticularly preferred liquid epoxy resins generally possess an n valueaveraging less than about 1.0. illustrative examples by standard tradedesignations of particularly useful commercially available epoxy resinsinclude: Epi-Rez 508 and Epi-Rez 510 (Celanese Coatings) ERLA 2256(Union Carbide), ERLA 4617 (Union Carbide), and Epon (Shell) epoxyresins.

Epoxy novolac resins formed by the reacting of epichlorohydrin withphenol-formaldehyde resins are also particularly preferred thermosettingresins. An illustrative example of a highly useful resin is Epi-Rez 5155epoxy novolac resin (Celanese Coatings).

A variety of epoxy resin curing agents may be em- ,ployed in conjunctionwith the epoxy resin. The curing or hardening of the epoxy resintypically involves fur- .ther reaction of the epoxy or hydroxyl groupsto cause molecular chain growth and cross-linking. The term Ycuringagent as used herein is accordingly defined to include the varioushardeners of the co-reactant type. Illustrative classes of known epoxycuring agents which may be utilized include aliphatic and aromaticamines,

polyamides, tertiary amines, amine adducts, acid anhydrides, acids,aldehyde condensation products, and Lewis acid type catalysts, such asboron trifluoride. The preferred epoxy curing agents for use with theepoxy resin are acid anhydrides (e.g. hexahydrophthalic acid andmethylbicyclo[2.2. l ]heptenel l -dicarboxylic anhydride isomersmarketed under the designation Nadic Methyl Anhydride by the AlliedChemical Company), and aromatic amines (e.g., meta-phenylene diamine anddimethylaniline).

The solventless system comprising an A-stage thermosetting may beprovided at a moderately elevated temperature during the impregnationstep of the process in order to impart the required viscosity to thesame. The exact temperature selected will vary with the specific systemselected as will be apparent to those skilled in the art. Resin systemtemperatures commonly range from about 25 to 100 C. at the time ofimpregnation. Those resin systems which exhibit a substantial pot lifeat the impregnation temperature are preferred.

The technique utilized to force the resin system into intimateassociation with multifilament fiber bundles of the ribbon may bevaried. It is essential, however, that the impregnation techniqueselected results in no substantial diminution of the tensile propertiesof the carbonaceous bundles. In a preferred embodiment of the processthe resin system is initially applied to the ribbon by briefly passingthe ribbon through a vessel containing the same, and the ribbon bearingthe resin system adhering to its surface is next passed between a pairof parallel nip rollers. In addition to immersion the resin initiallymay be satisfactorily applied by spraying, extruding, etc., prior topassage between a pair of nip rollers. One of the nip rollers optionallymay be provided with a flat groove corresponding in width to the widthof the ribbon, and the other nip roller provided with a substantiallymatching raised surface which in combination with the grooved rollerprovides a rectangular gap for the ribbon. The force exerted by such niprolls causes the resin system to flow throughout the ribbon.Alternatively, the impregnation step may be accomplished through the useof poltrusion or other application technique capable of bringing out thedesired impregnation.

The carbonaceous ribbon while in intimate association with thesolventless system is next interposed between the outer surfaces of apair of flexible endless belts. The belts preferably have smoothnonporous surfaces, are relatively thin so as to permit efficient heattransfer therethrough in the heating zone as described hereafter, andare capable of being readily stripped from a ribbon impregnated with atacky thermosetting resin. The belts are capable of withstanding thetemperatures employed in the subsequent heating zone, are capable ofwithstanding wash solvents, and may be formed from a variety ofmaterials. Preferred endless belts are formed from fiberglass reinforcedpolytetrafluoroethylene sheets having a thickness of about 0.005 to0.030 inch. Flexible endless belts alternatively may be formed fromflexible metallic strips or other fiber reinforced flexible resinousmaterials. The width of the endless belts is greater than the width ofthe ribbon interposed therebetween (e.g., 0.5 to 2 inches or wider), sothat the ribbon has each of its surfaces completely covered by theendless belts. The ribbon is preferably interposed substantially at thecenter of each belt and is aligned in parallel with the edges of thebelts.

While interposed between the flexible belts, the resin impregnatedribbon is continuously passed in the direction of its length through asubstantially enclosed heating zone provided with a heated gaseousatmosphere wherein the belts and the ribbon are looped in a single wrapabout each of a multiplicity of rotating spaced parallel rollers whereinthe inner surfaces of the belts are in alternating contact with therollers as the belts and the ribbon progress through the heating zone.The heating zone. may be relatively compact and provided with aplurality of pairs of spaced parallel rollers. As the belts and ribbonpass through the heating zone as a unitary body, the impregnated ribbonremains between the belts at a fixed location in the absence of slidaasntac mtissq sta t ly saspsn wi mnthc.

heating zone. As the belts and ribbon intermittently pass over therotating rollers a flexing action occurs and pressure is exerted onalternating sides of the ribbon which further improves the uniformity ofthe resin distribution throughout the ribbon. Each side of the ribbon isuniformly heated at the same temperature while passing through theheating zone.

The nature of heated gaseous atmosphere within the heating zone may bevaried. For instance, ordinary air may be employed. Alternatively, inertgases such as nitrogen may serve as the gaseous atmosphere. The gas ispreferably preheated prior to introduction into the heating zone such asby passing over electrical resistance heaters. Additionally, the gas ispreferably circulated within the heating zone by continuouslyintroducing and withdrawing a portion of the same.

While present in the heating zone, the thermosetting resin in intimateassociation with the ribbon is converted to a tacky B-stage consistency.The temperature of the gaseous atmosphere of the heating zone, as wellas the residence time during which the ribbon is within the heating zonewill vary depending upon the specific thermosetting resin undergoingpartial curing. Heating zone temperatures of about 75 to 175 C. arecommonly selected, and preferably the temperature of the gaseousatmosphere within the heating zone is maintained at about 100 to 150 C.Satisfactory residence times in which to accomplish the desired partialcuring within the heating zone commonly range from about 2 to 30minutes, an preferably about 10 to 15 minutes.

Since the ribbon is positioned between the endless belts as it passesthrough the heating zone, no splitting of roping of the ribbon occurs asis common in the prior art when a resin impregnated ribbon is passedacross an unsupported span. The overall dimensious of the heating zonemay be substantially reduced. Additionally, any volatile components ofthe resin system, e.g., curing agents, are retained within the ribbon bythe adjoining belts, thereby making possible uniform curing of thethermosetting resin to the desired tacky consistency. Since the endlessbelts have a width greater than that of the ribbon, the resin systemnever contacts the rotating rollers present within the heating zone.

The resulting ribbon is continuously withdrawn from the heating zonewhile interposed between the flexible belts prior to a point in timewhen the thermosetting resin is advanced to a hard non-tacky C-stageconsistency. The resin in intimate association with the ribbon remainsin a tacky B-stage consistency at the time of its withdrawl from theheating zone.

The resin impregnated carbonaceous ribbon is next separated from theflexible endless belts and may be collected or directly utilized in theformation of carbon fiber reinforced composite structures. The endlessbelts following separation from the resin impregnated ribbon may bewashed with an appropriate solvent (e.g., acetone or methylene chloride)to remove any adhering resin and returned for further use.

The uniformly resin impregnated carbon fiber ribbons formed in thepresent process preferably contain about to 55 percent partially curedthermosetting resin by volume (preferably about to percent by volume)and about 45 to 65 percent carbon fiber by volume (preferably about topercent by volume).

The resin impregnated ribbon following its separation from the endlessflexible belts may be positioned 1291 releasable int rla sa hass l c noat e a The resin impregnated ribbons produced in the present processfind particular utility in the production of high performance compositestructures which are highly useful in the aerospace industry. Forinstance, impellers, turbine blades, and similar lightweight structuralcomponentsmay be formed by conventional filament winding, molding, orshaping techniques.

A representative apparatus arrangement for carrying out the process ofthe present invention is illustrated in the drawing. Carbonaceous ribbonhaving a width of 2.75 inches is continuously unwound from flangedbobbin 2 which is free to rotate about its central axis. Thecarbonaceous ribbon consists of 300 continuous multifilament yarnbundles which are arranged in parallel with each yarn bundle containingabout 400 filaments, having a twist of about 0.5 tpi, exhibiting a totaldenier of about 400, and a predominantly graphitic X-ray diffractionpattern. The yarn bundles are derived from an acrylonitrile homopolymerand contain in excess of 99 percent carbon by weight. An interlay 4 ofKraft paper is also continuously unwound from flanged bobbin 2 and isreceived by interlay takeup 6 which is rotated about its axis by adriven constant speed AC motor (not shown) having a spring-tensionedfriction plate. The unwinding of carbonaceous ribbon 1 from flangedbobbin 2 is accordingly assisted by the rotation of interlay takeup 6which exerts a pulling force on interlay 4.

The carbonaceous ribbon 1 following unwinding from flanged bobbin 1passes over three grooved idler rolls 8, 10, and 12 which serve tocenter the ribbon, eliminate splits, and equalize yarn density acrossthe web. Each of the grooved idler rolls 8, l0, and 12 has groove widthof 2.75 inches, a groove depth of 0.25 inch, and a diameter within thegroove of 3 inches. After leaving grooved idler roller 12 thecarbonaceous ribbon is wrapped about a series of four tensioning rollersl4, l6, l8, and each having a 6 inch diameter, which apply a uniformtension to the ribbon. The tension is adjusted by varying the weight 22on dancer arm 24 as the ribbon passes about idler rolls 26, 28, and 30each having a diameter of 6 inches. Dancer arm 24 controls the speed oftensioning rollers l4, 16, 18, and 20 as well as the speed of upper niproller 35 with all five of these rollers being driven by the samevariable speed motor (not shown) by means of a chain drive (not shown).

After leaving idler roller 30, the carbonaceous ribbon passes about adriven grooved dip roller 34 which is partially immersed in vessel 36which contains a liquid solventless system containing an A-stagethermosetting resin and a curing agent for the resin. The driven grooveddip roller 34 has groove width of 2.75 inches, a groove depth of 0. linch, and a diameter within the groove of 3 inches. The carbonaceousribbon bearing a coating of the solventless system next passes between apair of driven parallel nip rollers 35 and 38. The nip rollers 35 and 38serve to force the resin system comprising an A-stage thermosettingresin into intimate association with the multifllament fiber bundles ofthe ribbon. Dip roller 34, vessel 36, and nip rollers 35, and 38 areinternally heated by a recirculating ethylene glycol-water solutionwhich aids in maintaining the solventless resin system at the desiredviscosity.

The carbonaceous ribbon 40 in intimate association with the resin systemcomprising an A-stage thermosetting resin is next interposed between apair flexible endless belts 44 and 45. The endless belts 44 and 45 arenon-porous, have widths of 4 inches, and are composed ofpolytetrafluoroethylene coated fiberglass. Spring mounted idler rollers46 and 48 facilitate the interpositioning of the ribbon 40 between belts44 and 45. The impregnated carbonaceous ribbon interposed between thebelts passes as a flat unitary structure 50 over compression plate 52and into heating zone 54.

The heating zone 54 is provided in a forced air convection ovenmeasuring 3 X 3 X 2 feet having a top to bottom air flow. Cantileveredwithin the heating zone 54 are eight oven rollers 56, 58, 60, 62, 64,66, 68, and '70 having diameters of 6 inches which are driven by acommon motor (not shown) at a constant speed. The resin impregnatedribbon while interposed been the belts and present in heating zone 54 issuccessively wrapped about each of oven rollers 56, 58, 60, 62, 64', 66,68, and 70. The driven rollers 56, 58, 60, 62, 64, 66, 68 and 70 withinthe heating zone 54 are rotated at the same rate as grooved dip roller34 and lower nip roller 38. While passing through heating zone 54 thethermosetting resin in intimate association with the carbonaceous ribbonis advanced to a tacky B-stage consistency, and it is in this state whenit exits from heating zone 54 at opening 72.

After passing between a pair of driven exit nip rollers 74 and 76, whichare rotating at the same rate as the oven rollers, the resultingcarbonaceous ribbon 78 is separated from the endless flexible belts 42and 44. The exit nip rollers 74 and 76 serve to isolate the tensionexerted upon the ribbon within the oven from the takeup winding tension.The belts 42 and 44 pass through belt washing pans 80 and 82'containinga solvent for the resin system where any adhering resin is removed bythe aid of rotating brushes. Uniform tension is maintained upon endlessbelts 42 and 44 by dancer arm assemblies 84 and 86.

A releasable paper interlay 88 is continuously unwound from reel 90 andcontacts the surface of idler roller 92 prior to the arrival of theresulting thermosetting resin impregnated carbonaceous ribbon 78. Theinterlay 88 hearing the tacky thennosetting resin impregnatedcarbonaceous ribbon 78 next passes about tensioning arm 94 and is woundupon flanged bobbin 96.

The following examples are given as more specific illustrations of theinvention. It should be understood, however, that the invention is notlimited to the specific details set forth in the examples. Reference ismade in the examples to the drawing.

EXAMPLE I The solventless system provided in dip pan 36 contained partsby weight of epoxy novolac resin formed by reacting epichlorohydrin witha phenolformaldehyde resin, and 88 parts by weight of an anhydridecuring agent. The solventless system at room temperature (i.e., 25 C.)exhibited a viscosity of about 100,000 cps. Internally heated dip roller34, vessel 36, and nip rollers 35 and 38 were maintained at 50 C. duringthe resin impregnation step at which temperature the resin systemexhibited a viscosity of about 1,000 cps. The gap between nip rollers 35and 38 was 0.008 inch.

The carbonaceous ribbon was passed through apparatus at a rate of 20inches per minute, and was present in heating zone 54 for a residencetime of 13.5 minutes which was maintained at a uniform temperature of132 C.

The resulting carbonaceous ribbon was uniformly impregnated with thetacky B-stage epoxy resin and consisted of about 42.6 percent of volumeresin, and about 57.4 percent by volume carbon fiber.

EXAMPLE ll The solventless system provided in dip pan 36 contained 100parts by weight of epoxy resin formed by reacting bisphenol A withepichlorohydrin, and 35 parts by weight of an amine curing agent. Thesolventless system at room temperature (i.e., 25 C.) was substantiallynon-flowable. Internally heated dip' roller 34, vessel 36, and niprollers 35 and 38 were maintained at 78 C. during the resin impregnationstep at which temperature the resin system exhibited a viscosity ofabout 2,000 cps. The gap between nip rollers 35 and 38 was 0.0l inch.

The carbonaceous ribbon was passed through the apparatus at a rate of 20inches per minute, and was present in heating zone 54 for a residencetime of 13.5 minutes which was maintained at a uniform temperature of125 C.

The resulting carbonaceous ribbon was uniformly impregnated with thetacky B-stage epoxy resin and consisted of about 45 percent by volumeresin, and 55 percent by volume carbon fiber.

Although the invention has been described with preferred embodiments, itis to be understood that variations and modifications may be resorted toas will be apparent to those skilled in the art. Such variations andmodifications are to be considered within the purview and scope of theclaims appended hereto.

We claim:

1. An improved process for the production of a uniformly resinimpregnated ribbon of a carbonaceous fibrous material which is suitablefor use in the manufacture of carbon fiber reinforced compositestructures comprising:

a. continuously conveying to an impregnation zone a carbonaceous fibrousribbon containing at least about 90 percent carbon by weight,

b. forcing a liquid solventless system having a viscosity of about 500to l0,000 cps, comprising an A- stage thermosetting resin into intimateassociation with said carbonaceous fibrous ribbon while present in saidimpregnation zone,

c. interposing said ribbon while in intimate association with saidsolventless system between the outer surfaces of a pair of flexibleendless belts having a non porous surface and a width greater than thatof said ribbon,

d. continuously passing said ribbon in the direction of its length whileinterposed between said flexible endless belts through a substantiallyenclosed heating zone provided with a heated gaseous atmosphere whilesubstantially suspended therein wherein said belts and said ribbon arelooped in a single wrap about each of a multiplicity of rotatingparallel rollers wherein the inner surfaces of said belts are inalternating contact with said rollers as said belts and said ribbonprogress through said heating zone with said ribbon being out of contactwith said rollers and wherein said thermosetting resin in intimateassociation with said ribbon is converted to a B-stage consistency,

e. continuously withdrawing said ribbon from said heating zone whileinterposed between said outer surfaces of said pair of flexible endlessbelts and while said thermosetting resin in intimate association withsaid ribbon remains in a B-stage consistency, and

f. separating said resulting resin impregnated carbonaceous fibrousribbon from said flexible endless belts.

2. An improved process according to claim 1 wherein said carbonaceousfibrous ribbon comprises a plurality of substantially parallelmultifilament fiber bundles.

3. An improved process according to claim 1 wherein said carbonaceousfibrous ribbon is a tow.

4. An improved process according to claim 1 wherein said carbonaceousfibrous ribbon contains at least about 95 percent carbon by weight andexhibits a predominantly graphitic X-ray diffraction pattern.

5. An improved process according to claim 1 wherein said liquidsolventless system comprising an A-stage thermosetting resin has aviscosity of about 1,000 to 3,000 cps.

6. An improved process according to claim 1 wherein said solventlesssystem comprising an A-stage thermosetting resin is forced into intimateassociation with said carbonaceous fibrous ribbon by passing said ribbonbearing said system upon its surface through a pair of rotating parallelnip rollers.

7. An improved process according to claim 1 wherein said solventlesssystem comprises an A-stage epoxy resin and a curing agent for saidresin.

8. An improved process according to claim 7 wherein said epoxy resin isa condensation product of bisphenol A and epichlorohydrin.

9. An improved process according to claim 7 wherein said epoxy resin isan epoxy novolac resin formed by the reacting of epichlorohydrin with aphenolformaldehyde resin.

10. An improved process according to claim I wherein said resultinguniformly resin impregnated carbonaceous fibrous ribbon contains about35 to percent B-stage thermosetting resin by volume, and about 45 topercent carbon fiber by volume.

11. An improved process for the production of a uniformly resinimpregnated ribbon of a carbonaceous fibrous material which is suitablefor use in the manufacture of carbon fiber reinforced compositestructures comprising:

a. continuously conveying to an impregnation zone a carbonaceous fibrousribbon containing at least about percent carbon by weight,

b. forcing a liquid solventless system having a viscosity of about 1,000to 3,000 cps. comprising an A- stage thermosetting epoxy resin and acuring agent for said resin into intimate association with saidcarbonaceous fibrous ribbon while present in said impregnation zone,

c. interposing said ribbon while in intimate association with saidsolventless system between the outer surfaces of a pair of flexibleendless belts having a non porous surface and a width greater than thatof said ribbon,

d. continuously passing said ribbon in the direction of its length whileinterposed between said flexible endless belts through a substantiallyenclosed heating zone provided with a heated gaseous atmosphere at atemperature of about 75 to 175 C. while substantially suspended thereinwherein said belts and said ribbon are looped in a single wrap abouteach of a multiplicity of rotating parallel rollers wherein the innersurfaces of said belts are in alternating contact with said rollers assaid belts and said ribbon progress through said heating zone with saidribbon being out of contact with said rollers and wherein saidthermosetting epoxy resin in intimate association with said ribbon isconverted to a B-stage consistency,

e. continuously withdrawing said ribbon from said heating zone whileinterposed between said outer surfaces of said pair of flexible endlessbelts and while said thermosetting epoxy resin in intimate associationwith said ribbon remains in a B-stage consistency, and

f. separating said resulting epoxy resin impregnated carbonaceousfibrous ribbon from said flexible endless belts.

12. An improved process according to claim 11 wherein said carbonaceousfibrous ribbon comprises a plurality of substantially parallelmultifilament fiber bundles.

13. An improved process according to claim 11 wherein said carbonaceousfibrous ribbon is a tow.

14. An improved process according to claim 11 wherein said carbonaceousfibrous ribbon contains at least about percent carbon by weight andexhibits a predominantly graphitic X-ray diffraction pattern.

15. An improved process according to claim 11 wherein said heatedgaseous atmosphere provided within said heating zone has a temperatureof about to C.

16. An improved process according to claim 11 wherein said solventlesssystem comprising an A-stage thermosetting epoxy resin and a curingagent for said resin is forced into intimate association with saidcarbonaceous fibrous ribbon by passing said ribbon bearing said systemupon its surface through a pair of rotating parallel nip rollers.

17. An improved process according to claim 11 wherein said epoxy resinis a condensation product of bisphenol A and epichlorohydrin.

18. An improved process according to claim 1 wherein said epoxy resin isan epoxy novolac resin fonned by the reacting of epichlorohydrin with aphenol-formaldehyde resin.

19. An improved process according to claim 11 wherein said resultinguniformly epoxy resin impregnated carbonaceous fibrous ribbon containsabout 35 to 55 percent B-stage thermosetting epoxy resin by volume, andabout 45 to 65 percent carbon fiber by volume.

1. AN IMPROVED PROCESS FOR THE PRODUCTION OF A UNIFORMLY RESINIMPREGNATED RIBBON OF A CARBONACEOUS FIBROUS MATERIAL WHICH IS SUITABLEFOR USE IN THE MANUFACTURE OF CARBON FIBER REINFORCED COMPOSITESTRUCTURES COMPRISING: A. CONTINUOUSLY CONVEYING TO AN IMPREGNATION ZONETO CARBONACEOUS FIBROUS RIBBON CONTAINING AT LEAST ABOUT 90 PERCENTCARBON BY WEIGHT, B. FORCING A LIQUID SOLVENTLESS SYSTEM HAVING AVISCOSITY OF ABOUT 500 TO 10,000 CPS, COMPRISING AN A-STAGETHERMOSETTING RESIN INTO INTIMATE ASSOCIATION WITH SAID CARBONACEOUSFIBROUS RIBBON WHILE PRESENT IN SAID IMPREGNATION ZONE, C. INTERPOSINGSAID RIBBON WHILE IN INTIMATE ASSOCIATION WITH SAID SOLVENTLESS SYSTEMBETWEEN THE OUTER SURFACES OF A PAIR OF FLEXIBLE ENDLESS BELTS HAVING ANON POROUS SURFACE AND A WIDTH GREATER THAN THAT OF SAID RIBBON, D.CONNTINUOUSLY PASSING SAID RIBBON IN THE DIRECTION OF ITS LENGTH WHILEINTERPOSED BETWEEN SAID FLEXIBLE ENDLESS BELTS THROUGH A SUBSTANTIALLYENCLOSED HEATING ZONE PROVIDED WITH A HEATED GASEOUS ATMOSPHERE WHILESUBSTANTIALLY SUSPENDED THEREIN WHEREIN SAID BELTS AND SAID RIBBON ARELOOPED IN A SINGLE WRAP ABOUT EACH OF A MULTIPLICITY OF ROTATINGPARALLEL ROLLERS WHEREIN THE INNER SURFACES OF SAID BELTS ARE INALTERNATING CONTACT WITH SAID ROLLERS AS SAID BELTS AND SAID RIBBONPROGRESS THROUGH SAID HEATING ZONE WITH SAID RIBBON BEING OUT OF CONTACTWITH SAID ROLLERS AND WHEREIN SAID THERMOSETTING RESIN IN INTIMATEASSOCIATION WITH SAID RIBBON IS CONVERTED TO A B-STAGE CONSISTENCY. E.CONTINUOUSLY WITHDRAWING SAID RIBBON FROM SAID HEATING ZONE WHILEINTERPOSED BETWEEN SAID OUTER SURFACES OF SAID PAIR OF FLEXIBLE ENDLESSBELTS AND WHILE SAID THERMOSETTING RESIN IN INTIMATE ASSOCIATION WITHSAID RIBBON REMAINS IN A B-STAGE CONSISTENCY, AND F. SEPARATING SAIDRESULTING RESIN IMPREGNATED CARBONACEOUS FIBROUS RIBBON FROM SAIDFLEXIBLE ENDLESS BELTS.
 2. An improved process according to claim 1wherein said carbonaceous fibrous ribbon comprises a plurality ofsubstantially parallel multifilament fiber bundles.
 3. An improvedprocess according to claim 1 wherein said carbonaceous fibrous ribbon isa tow.
 4. An improved process according to claim 1 wherein saidcarbonaceous fibrous ribbon contains at least about 95 percent carbon byweight and exhibits a predominantly graphitic X-ray diffraction pattern.5. An improved process according to claim 1 wherein said liquidsolventless system comprising an A-stage thermosetting resin has aviscosity of about 1,000 to 3,000 cps.
 6. An improved process accordingto claim 1 wherein said solventless system comprising an A-stagethermosetting resin is forced into intimate association with saidcarbonaceous fibrous ribbon by passing said ribbon bearing said systemupon its surface through a pair of rotating parallel nip rollers.
 7. Animproved process according to claim 1 wherein said solventless systemcomprises an A-stage epoxy resin and a curing agent for said resin. 8.An improved process according to claim 7 wherein said epoxy resin is acondensation product of bisphenol A and epichlorohydrin.
 9. An improvedprocess according to claim 7 wherein said epoxy resin is an epoxynovolac resin formed by the reacting of epichlorohydrin with aphenol-formaldehyde resin.
 10. An improved process according to claim 1wherein said resulting uniformly resin impregnated carbonaceous fibrousribbon contains about 35 to 55 percent B-stage thermosetting resin byvolume, and about 45 to 65 percent carbon fiber by volume.
 11. Animproved process for the production of a uniformly resin impregnatedribbon of a carbonaceous fibrous material which is suitable for use inthe manufacture of carbon fiber reinforced composite structurescomprising: a. continuously conveying to an impregnation zone acarbonaceous fibrous ribbon containing at least about 90 percent carbonby weight, b. forcing a liquid solventless system having a viscosity ofabout 1,000 to 3,000 cps. comprising an A-stage thermosetting epoxyresin and a curing agent for said resin into intimate association withsaid carbonaceous fibrous ribbon while present in said impregnationzone, c. interposing said ribbon while in intimate association with saidsolventless system between the outer surfaces of a pair of flexibleendless belts having a non porous surface and a width greater than thatof said ribbon, d. continuously passing said ribbon in the direction ofits length while interposed between said flexible endless belts througha substantially enclosed heating zone provided with a heated gaseousatmosphere at a temperature of about 75* to 175* C. while substantiallysuspended therein wherein said belts and said ribbon are looped in asingle wrap about each of a multiplicity of rotating parallel rollerswherein the inner surfaces of said belts are in alternating contact withsaid rollers as said belts and said ribbon progress through said heatingzone with said ribbon being out of contact with said rollers and whereinsaid thermosetting epoxy resin in intimate association with said ribbonis converted to a B-stage consistency, e. continuously withdrawing saidribbon from said heating zone while interposed between said outersurfaces of said pair of flexible endless belts and while saidthermosetting epoxy resin in intimate aSsociation with said ribbonremains in a B-stage consistency, and f. separating said resulting epoxyresin impregnated carbonaceous fibrous ribbon from said flexible endlessbelts.
 12. An improved process according to claim 11 wherein saidcarbonaceous fibrous ribbon comprises a plurality of substantiallyparallel multifilament fiber bundles.
 13. An improved process accordingto claim 11 wherein said carbonaceous fibrous ribbon is a tow.
 14. Animproved process according to claim 11 wherein said carbonaceous fibrousribbon contains at least about 95 percent carbon by weight and exhibitsa predominantly graphitic X-ray diffraction pattern.
 15. An improvedprocess according to claim 11 wherein said heated gaseous atmosphereprovided within said heating zone has a temperature of about 100* to150* C.
 16. An improved process according to claim 11 wherein saidsolventless system comprising an A-stage thermosetting epoxy resin and acuring agent for said resin is forced into intimate association withsaid carbonaceous fibrous ribbon by passing said ribbon bearing saidsystem upon its surface through a pair of rotating parallel nip rollers.17. An improved process according to claim 11 wherein said epoxy resinis a condensation product of bisphenol A and epichlorohydrin.
 18. Animproved process according to claim 1 wherein said epoxy resin is anepoxy novolac resin formed by the reacting of epichlorohydrin with aphenol-formaldehyde resin.
 19. An improved process according to claim 11wherein said resulting uniformly epoxy resin impregnated carbonaceousfibrous ribbon contains about 35 to 55 percent B-stage thermosettingepoxy resin by volume, and about 45 to 65 percent carbon fiber byvolume.